The present invention relates to a novel image data compression or expansion method and apparatus, and more particularly, to an image transmission system and a monitoring system using the method and apparatus.
To transmit image data on a communication line or record the image data in a recording device, generally, the image data must be compressed by any means because the data amount of original image data is too large. As a representative image data compression method, the H.261 method of the ITU-T (International Telecommunication Union-Telecommunication Standardization Sector) standards has been known and is put into practical use.
This method compression-encodes an image signal to data of a low bit rate of several 10 to 100 kbps, to transmit the image data on a communication line, to realize a so-called picturephone. The method utilizes time sequential information compression by motion compensation and spatial information compression by DCT (Discrete Cosine Transformation).
Further, image data compression methods based on the JPEG, MPEG1 and the like are known. These methods perform image data compression processing so as to maintain a constant frame rate (the number of frames within a fixed period).
Generally, upon image data compression, if the content of image is fine (many high frequency components are included), or the motion of the image is fast, the image data cannot be greatly compressed. Accordingly, when image data is compression-encoded to data with several 10 to 100 kbps transmission speed by the above-mentioned H.261 method, generally, in a scene where the image is not so fine and the motion is slow, the frame rate (the number of frames within a fixed period) is raised (increased), on the other hand, in a scene where the image is fine and the motion is fast, the frame rate is lowered (reduced).
As the frame rate is low (the number of frames is small) in a scene where the image is fine and the motion is fast, the movement displayed on a display device of a transmission destination is intermittent and unnatural. Further, generally, upon control to increase the frame rate in the fast-motion scene, the image quality of the image itself is degraded.
In this manner, with regard to a scene with large data amount even if compressed, where the image is fine and the motion is fast, the image data compression processing by the above-described conventional art merely reduces the data transfer speed while degrading the image quality of the image itself, or merely obtains a constant frame rate. The point of improvement in image quality of such scene where the image is fine and the motion is fast has not been taken into consideration at all. That is, in the above conventional techniques cannot obtain an image with excellent image quality regarding a scene where the image is fine and the motion is fast.
Generally, in a remote monitoring system to monitor transmission of on-site image by using a telephone line, an image with large amount of motion or change is especially significant as an image of abnormal status such as somebody""s intrusion or fire. Further, in such remote monitoring system, it is desired to compress and transfer even an image with large amount of motion or change with sufficient image quality. That is, in a scene where the motion is not fast and the amount of change is small, the frame rate can be low, but in a scene where the amount of change is large and the motion is fast, corresponding to an abnormal situation, it is necessary to control the transmission such that the frame rate is not reduced and sufficient image quality can be maintained.
However, as described above, in the conventional technique based on the H.261 method or the like, the frame rate is high in a scene where the motion is slow, which is not so significant for the monitoring system, while the frame rate is lowered or the image quality is degraded in a scene with fast motion, which is significant for the monitoring system.
For this reason, the present invention has its object to provide image data compression or expansion method and apparatus and image transmission system using the method and apparatus, which solve the problems in the conventional techniques, improve the image quality of a scene where the image greatly changes and the motion is fast, and reduce the entire image data.
Further, another object of the present invention is to apply the above-described present invention to a remote monitoring system, to provide an excellent remote monitoring system, in which the image quality is not degraded in a scene where the motion is fast, significant for the monitoring system.
According to the present invention, to attain the aforementioned objects, the motion and change are detected in each scene, and the frame rate (the number of frames within a fixed period) is controlled to be higher in a scene with large change or fast motion, than in a scene with small change and motion.
More specifically, the above objects are attained by providing an image data compression apparatus which compresses input image data and outputs compressed image data, comprising: compression processing means for compression-processing input image data; image change detection means for detecting a change on image based on the input image data; frame rate control means for controlling a frame rate of outputted compressed image data obtained by compression-processing image data; and means for controlling the frame rate of outputted compressed image data such that the frame rate in a scene where the image change is small is lower than the frame rate in a scene where the image change is large, in accordance with the situation of the change on image detected by the image change detection means.
Further, according to the present invention, in the image data compression apparatus, the image change detection means comprises change amount detection means for detecting a change amount between images in the input image data.
Further, according to the present invention, in the image data compression apparatus, the image change detection means comprises motion amount detection means for detecting a motion amount on image in the input image data.
Further, according to the present invention, in the image data compression apparatus, the change amount detection means comprises reference image storage means for storing predetermined image data as a reference image, and arithmetic processing means for performing predetermined arithmetic processing between the input image data and the image data stored in the reference image storage means.
Further, according to the present invention, in the image data compression apparatus, the arithmetic processing means is subtraction processing means for performing subtraction.
Further, according to the present invention, in the image data compression apparatus, the motion amount detection means comprises reference image storage means for storing predetermined image data as a reference image and motion vector detection means for detecting a motion vector of input image data with respect to the image data stored in the reference image storage means.
Further, according to the present invention, in the image data compression apparatus, the frame rate control means comprises switching control means for performing or not performing compression encoding on image data in one-frame units, and the frame rate control means does not perform compression encoding on image data with a small change amount or motion amount, by using the switching control means, in accordance with the result of detection by the change amount detection means or that by the motion amount detection means.
Further, according to the present invention, the image data compression apparatus further comprises synthesizing means for synthesizing information on the frame rate of the compressed image data, controlled by the frame rate control means, wherein the information on the frame rate is added to the compressed image data, and the compressed image data is outputted.
Further, according to the present invention, in the image data compression apparatus, the information on the frame rate is information on the number of frames thinned out for reducing the frame rate or information on time interval between thinned frames.
Further, according to the present invention, the image data compression apparatus further comprises recording means for recording input image at predetermined time intervals, wherein the image data compression is performed on the image recorded in the recording means.
Further, according to the present invention, the image data compression apparatus further comprises recording means for recording compression-encoded compressed image data, wherein the speed of outputting the compression-encoded imaged data is controlled by controlling reading from the recording means.
Further, according to the present invention, the above objects are attained by providing an image data expansion apparatus, which inputs and expands compressed image data outputted from the image data compression apparatus, comprising: decoding means for decoding compressed image data at a frame rate controlled to be lower in a scene where the change is small, than in a scene where the change is large; and expansion means for expanding the compressed image data decoded by the decoding means, wherein the input image data is reproduced such that the frame rate is lower in a scene where the change between images is small than the frame rate in a scene where the change between images is large.
Further, according to the present invention, the above objects are attained by providing an image data expansion apparatus, which inputs and expands compressed image data outputted from the image data compression apparatus, comprising: decoding means for decoding compressed image data at a frame rate controlled to be lower in a scene where the change is small than in a scene where the change is large; expansion means for expanding the compressed image data decoded by the decoding means, wherein the input image data being reproduced such that the frame rate is lower in a scene where the change between images is small than the frame rate in a scene where the change between images is large; and image interpolation means for generating an interpolation image from the input predetermined compressed image data, in accordance with the information on the frame rate outputted with the compression image data, wherein the reproduced input image data is interpolated with an interpolation image generated by interpolation processing by the image interpolation means, and the interpolated image data is outputted.
Further, according to the present invention, the above objects are attained by providing an image data compression method for compressing input image data and outputting compressed image data, comprising the steps of: detecting a change on image based on the input image data; controlling a frame rate of outputted compressed image data obtained by compression-processing image data such that the frame rate in a scene where the image change is small is lower than the frame rate in a scene where the image change is large, in accordance with the situation of the detected the change on image; and outputting the compression-processed image data.
Further, according to the present invention, in the image data compression method, detection of the change on image is made by detecting a change amount between images in the input image data.
Further, according to the present invention, in the image data compression method, detection of the change on image is made by detecting an motion change amount on image in the input image data.
Further, according to the present invention, in the image data compression method, detection of the change is made by arithmetic processing between images in the input image data.
Further, according to the present invention, in the image data compression method, detection of the change is made by detecting a motion vector of the input image data.
Further, according to the present invention, the image data compression method further comprises the step of synthesizing information on the controlled frame rate to the output compressed image data.
Further, according to the present invention, in the image data compression method, the information on the frame rate is information on the number of frames thinned out to reduce the frame rate or information on time interval between thinned frames.
Further, according to the present invention, the above objects are attained by providing an image data expansion method for inputting and expanding compressed image data, outputted by the image data compression method, comprising the steps of: decoding compressed image data, at the frame rate controlled to be lower in the scene where the image change is small than in the scene where the image change is large; and expanding the decoded compressed image data such that the frame rate in the scene where the change between images is small is lower than that in the scene where the change between images is large.
Further, according to the present invention, the above objects are attained by providing an image data expansion method for inputting and expanding compressed image data, outputted by the image data compression method, comprising the steps of: decoding the compressed image data at the frame rate controlled to be lower in the scene where the image change is small than in the scene where the image change is large; reproducing the input image data by expanding the decoded compressed image data such that the frame rate in the scene where the image change is small is lower than that in the scene where the image change is large; and generating an interpolation image from input predetermined compressed image data, in accordance with information on the frame rate, received with the compressed image data, and interpolating the reproduced input image with the generated interpolation image and outputting the interpolated image.
Further, according to the present invention, the above objects are attained by providing an image transmission system which performs image data communication by using an image data compression apparatus and an image data expansion apparatus, comprising: the image data compression apparatus, which compresses input image data and outputs compressed image data; transmission means for transmitting the compressed image data, outputted from the compression apparatus, on a predetermined line; reception means for receiving the compressed image data transmitted via the transmission means; and the image data expansion apparatus, which expands the compressed image data received by the reception means.
Further, according to the present invention, the above objects are attained by providing a monitoring system which performs image data communication by using an image data compression apparatus and an image data expansion apparatus, comprising: image data output means for obtaining an image of a monitoring object and outputting image data; the image data compression apparatus, which compresses input image data, from the image data output means, and outputs compressed image data; transfer means for transferring the compressed image data outputted from the image data compression apparatus; the image data expansion apparatus, which expands the compressed image data transferred via the transfer means; and a display device which displays the image data expanded by the image data expansion apparatus.
Further, according to the present invention, in the monitoring system, the transfer means comprises a communication line for transmitting image data.
Further, according to the present invention, in the monitoring system, the transfer means comprises a recording medium for recording image data.
Other features and advantages of the present invention will be apparent from the following description taken in conjunction with the accompanying drawings, in which like reference characters designate the same name or similar parts throughout the figures thereof.